1. Field of the Invention
The present invention relates to a device for preparing a medicinal liquid by combining a first liquid substance contained in a first variable-volume chamber and a second substance contained in a second chamber, this device comprising means for supporting the first and second chambers, means for allowing these chambers to communicate with each other and a movable member for applying a suitable force to reduce the volume of the said first chamber in order to transfer the liquid from the first chamber to the second chamber. It also relates to a unit for preparing and injecting a medicinal liquid and to a method for preserving a solution of medicament for injection.
2. Description of Related Art
Several devices of this kind have already been proposed for the purpose of mixing two substances, particularly for preparing a medicinal liquid with a short storage life. Such devices can be used by nursing staff or by the patient him or herself to prepare the liquid by mixing the two substances at the desired time.
Such a device was proposed in WO 97/46203, more particularly for reconstituting a medicinal liquid by diluting or suspending a solid substance contained in a vial with the aid of a liquid contained in a chamber and introduced into the vial through a needle, the liquid being pushed by sliding a plunger along the inside of the chamber of liquid, after which the diluted substance is returned to the chamber.
Another proposal, made in U.S. Pat. No. 4,338,980, was for a device for filling an injector from the front from a vial containing the medicine, the bottom of which comprises a plunger which is pushed towards the dispensing opening of the injector. Under pressure, the liquid enters the injector through this orifice and the plunger of the injector moves back as the liquid is transferred from the vial into the injector.
Besides the cases cited above, there are medicines that contain injectable proteins to which a bactericidal liquid must be added. However, this bactericidal liquid must not be placed in contact with the proteins for any length of time before the medicine is used, as for example at the manufacturing stage, which is why the medicinal liquid is produced and packaged without the bactericidal liquid, which must be added only a short time before the medicinal liquid is used.
Many injectable medicaments, such as proteins, must be administered repeatedly over a given prolonged period. Such medicaments are often formulated in solutions contained in vials which contain sufficient material for multiple injections (for example, for one to two weeks). These vials can be filled and sealed under sterile conditions, in such a manner that the medicament solution has a considerable shelf life (usually at least 12 months, and sometimes as long as 24 months). However, once the seal of the vial has been compromised (e.g. at the time of first use), the shelf life of such vials is very short, due to bacterial contamination and growth. To attempt to overcome this problem, a bacteriostat has been added to the medicament solution at the time the vial is filled and sealed. This suffers the considerable drawback that many bacteriostats interact negatively with medicaments in solution over prolonged periods, with the result that the medicament may be degraded or precipitated due to interaction with the bacteriostat while the vial sits on the shelf.
The disadvantage of existing devices arises from the fact that they necessitate relatively complicated handling. Furthermore, the amount of liquid transferred depends on the displacement of the plunger, and there is no guarantee that the required amplitude of this displacement has actually been complied with, given that the displacement is indicated by marks which there is no compulsion on the user to observe. As a result there is no certainty as to the amount of liquid transferred because such amount depends on whether or not the required displacement is complied with, which can obviously have serious consequences on the patient.